Diabetes

ABC of Diabetes
by Peter J. Watkins

Hypoglycaemia

Hypoglycaemia is the major hazard of insulin treatment, and problems have increased in the drive to achieve “tight control”. Patients may experience the symptoms of hypoglycaemia when the blood concentration is less than 3·0 mmol/l. However, individual susceptibility varies considerably and it is interesting that some patients whose control has been persistently very poor for long periods appear to experience hypoglycaemic symptoms at levels a little above this. The risks of hazard from hypoglycaemia are small in most patients, but because they exist at all, patients taking insulin are barred from certain occupations such as driving trains or buses. All patients taking insulin whose diabetes is reasonably well controlled will experience hypoglycaemia at some stage. At its mildest, it is no more than a slight inconvenience, but at its severest, when unconsciousness can occur, it is both a hazard and an embarrassment. Furthermore, manipulative patients can use hypoglycaemia to threaten family and friends. This sword of Damocles is ever present once insulin treatment has started, and the need to use measures to avoid it requires constant, indeed lifelong, vigilance. Hypoglycaemia occurs infrequently in patients taking oral hypoglycaemics.

Symptoms

Most patients experience the early warning symptoms of hypoglycaemia and can take sugar before more serious symptoms develop. These warning symptoms are well known and are described in the box. Tremulousness and sweating are by far the commonest symptoms, while circumoral paraesthesiae is the most specific. Many patients have highly individual symptoms of hypoglycaemia which range from quite inexplicable sensations to peripheral paraesthesiae. In three patients carpal tunnel compression resulted in tingling fingers when they were hypoglycaemic, representing their sole warning. Neuroglyopenic symptoms and diminished cognitive function follow if corrective action is not taken, with progressive confusion and eventually unconsciousness and occasionally convulsions. There is a prolonged debate as to whether recurrent hypoglycaemia causes long-term intellectual decline; the evidence in general is unconvincing although major and recurrent episodes in childhood may have an adverse effect in this regard.

Patients who become unconscious from hypoglycaemia need urgent treatment. Brain damage and death do not normally occur because the blood glucose concentration tends to increase spontaneously as the effect of the insulin wears off and the normal counter-regulatory responses become effective. Many diabetics, especially children, need reassurance that they will not die in their sleep. Nevertheless, a very small number of otherwise unexplained deaths at night have been reported in Type 1 diabetic patients (described as the “dead in bed” syndrome) and no precise cause has ever been established. Deaths from prolonged hypoglycaemia are most likely to occur after insulin overdoses, as a result either of a suicide or murder attempt, but even in these circumstances most patients recover.

Diminished awareness of hypoglycaemia

This is the problem which all insulin treated patients dread, and at some stage it affects up to one quarter of Type 1 diabetic patients. It occurs when patients do not experience the early warning symptoms and directly develop diminished cognitive function which prevents them from taking the required preventive action. In this situation, help is required from a third party. This commonly occurs in the home when friends and relations observe the person to be slow-witted with a vacant expression and perspiring face. They may be taciturn, truculent or even obstructive, sometimes refusing to take sugar when advised, although many learn to accept this advice. This state of cognitive impairment can persist for some considerable time, long enough for abnormal behaviour to be noticed during driving, even for several miles; shoppers in the High Street may be unaware that they are shoplifting. If corrective action is not taken, the more serious state of unconsciousness already described can occur.

Night-time hypoglycaemia is very common, usually occurring between 3 and 6 am. The blood glucose concentration often falls below the hypoglycaemic threshold; levels as low as 1·0 mmol/l are not rare, and are known to cause electroencephalogram abnormalities even in the absence of symptoms. Many people become very restless when hypoglycaemic; this is recognised most frequently by the spouse who takes the necessary remedial action. Profound sweating is common, sometimes necessitating a change of nightclothes or bedclothes and may be the only manifestation that hypoglycaemia has occurred. Convulsions are not rare, and some patients wake in the morning with a bitten tongue as the only indication that this may have occured.

Note: The rest of the chapter is omitted.